Thanks for reaching out.
The reason for that is because the cornerstone endpoint returns 404 which is unusual to cause by an update, because it’s been there since older versions. It could be due to security that blocks it, I did some initial checking with no luck. Perhaps you can backup your site before I do further testing? I like to disable everything and test it, it’s a lot from there so that staging might have your development site and testing it could alter what’s already there.